gnuserv allows you to attach to an already running Emacs. This allows
external programs to make use of Emacs' editing capabilities. It is
like GNU Emacs' emacsserver/server.el, but has many more features.
You do not need this package if you use XEmacs; it already includes
gnuserv and gnuclient. If you want to use gnuserv with both GNU Emacs
and XEmacs, you will only be able to use the alternative
/usr/bin/gnuclient with one flavor of emacs; you will have to use
either gnuclient.xemacs or gnuclient.emacs for the other flavor.